1. Field of the Invention
The present invention relates to a depolarizing film and a method for production thereof. The depolarizing film may be used in combination with a polarizer or the like to form an optical film. The depolarizing film or the optical film is preferably used on the viewer side of a liquid crystal display for vehicle-mounted applications, mobile applications, information display applications, or the like.
2. Description of the Related Art
Liquid crystal displays are widely used in portable terminals such as cellular phones and personal digital assistants (PDAs), audio visual (AV) devices, game machines, digital cameras, film cameras, car navigation systems, and watches. Such liquid crystal display-equipped devices are used not only indoors but also outdoors. Such liquid crystal displays use liquid crystal switching to visualize changes in polarization state, and based on the display principle, the liquid crystal displays use polarizers and emit linearly polarized light.
In recent years, people occasionally wear sunglasses outdoors. In particular, polarizing sunglasses are preferably used in viewpoint of reduction of reflected light from water sides, road surfaces, and buildings. In some cases, however, people wearing polarizing sunglasses have difficulty seeing things on liquid crystal display-equipped devices, depending on the angle at which the people view the devices. In particular, displayed things become invisible, when the polarized light transmission axis of polarizing sunglasses is placed perpendicular to the polarized light transmission axis of the polarizer placed on the screen side of liquid crystal displays.
Concerning the problem with the visibility of liquid crystal displays for viewers wearing sunglasses, for example, it is proposed that a transparent cover layer comprising a birefringent material having a certain thickness distribution in the in-plane direction should be placed on the uppermost surface of a liquid crystal display (see JP-A No. 2005-148119). In the process of placing the transparent cover layer on the uppermost surface of a liquid crystal display as described in JP-A No. 2005-148119, however, it is necessary to precisely control the absorption axis of the viewer side polarizer and the slow axis of the transparent cover layer. In addition, since the transparent cover layer has to be shaped into a specific form, this technique has the problem of low productivity.